This application addresses broad challenge area (15): Translational Science, and specific Challenge Topic 15-DE-104: Functional Restoration of Salivary Glands. Hypofunction of salivary gland is a common pathological condition in patients with Sj"gren's syndrome or treated with radiotherapy for head and neck cancer. Current treatments can only temporarily relieve the symptoms, while regenerative therapies based on adult salivary gland stem cells have shown potential to restore salivary gland function in animal models. To improve the efficiency of these regenerative therapies, the molecular control of self-renewal, proliferation and differentiation of salivary gland stem cells need to be explored. Wnt/[unreadable]-catenin and Hedgehog intercellular signal pathways regulate activities of various adult stem cells, and are close related to homeostasis and regeneration of many renewable tissues, but whether they are also involved in these processes in salivary gland is unknown. For the first time, our preliminary data from genetic mouse models demonstrated that Wnt/[unreadable]-catenin signaling is active in adult salivary gland, and regulates differentiation and proliferation of salivary gland stem cells upstream of Hedgehog pathway. To explore the potential of manipulating Wnt and Hedgehog pathways for restoration of salivary gland function, we will: (1) Identify cell populations responding to Wnt and Hedgehog signals and trace their fate during homeostasis and regeneration of salivary gland with corresponding genetic reporter mouse models;(2) Determine whether transient activation of Wnt signaling promotes functional restoration of salivary gland after irradiation, transient Wnt activation will be achieved either in bi-transgenic mice over-expressing Wnt1 in basal epithelia upon doxycycline induction, or with recombinant R-Spondin protein which relieves endogenous Wnt inhibition;3) Determine whether transient activation of Sonic Hedgehog signaling promotes salivary gland functional restoration after local irradiation with bi-transgenic mice over-expressing Sonic Hedgehog in basal epithelia upon doxycycline induction. Given the essential roles of Wnt and Hedgehog signaling in various regenerative processes and our preliminary data on their roles in regulation of salivary gland stem cells, the proposed project will shed light on new regenerative strategies to restore the function of salivary gland. This application addresses broad challenge area (15): Translational Science, and specific Challenge Topic, 15-DE-104 Functional Restoration of Salivary Glands. We will explore the potential of manipulating Wnt and Hedgehog pathways for restoration of salivary gland function with inducible genetic mouse models and recombinant Wnt derepressor protein.